Process for producing pivalolactone



May 23, 1967 P. BORNER 3,321,490

PRQCESS FOR PRODUCING PIVALOLACTONE Filed July 12, 1965 FIG. 3.

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INVENTOR PETER BORNER DEZSOE STEINHERZ 3,321,490 Patented May 23, 1967 PROCESS FOR PRODUCING PIVALOLACTONE Peter Borner, Altiunen, Germany, assignor to Schering Airtiengcsellschaft, Berlin, Germany Filed July 12, 1965, Ser. No. 471,077

Claims priority, application Germany, July 22, 1964,

Sch 35,508 i 8 Claims. (Cl. 260-3433) It has been suggested to prepare pivalolactone by the reaction of a mixture of monohalogeno-pivalic acid and an anhydrous metallic base, or by heating of the anhydrous salts of alkali, strontium, and barium of monohalogeno-pivalic acid. In this process which is described in the German Auslegeschrift No. 1,167,809, inert highb'oiling solvents are used. Furthermore, in a process for preparing a,u-bis-chloromethyl-B-propiolactone is prepared by thermal decomposition of the anhydrous silveror leadsalts of the B,;8,;S"-trichloropivalic acid (see US. Patent No. 2,977,373. In an analogous procedure pivalolactone can be prepared by thermal decomposition of the dry, anhydrous silveror lead-salts or chloropivalic acid.

In the above named processeswith the exception of the use of silver salts, which are rather expensive in a commercial process-pivalolactone is obtained in yields of maximum 70% of the theory only. A particular disadvantage of these processes consists, moreover, in that upon increasing the amount of the mixture of metal bases and the chloropivalic acid or of the dry chloropivalic acid metal salts used in an inert solvent, the yield of the lactone is decreased. For example, in the pyrolysis of 200 g. of dry fine-grained chloropivalic acid lead salt in the temperature range of ISO-250 C. in a vacuum of 1 torr, pivalolactone is obtained in a yield of 68% of. the theory, while in the pyrolysis of 1000 g. of said salt under equal conditions the yield amounts to 52% only.

For the commercial production of pivalolactone from chloropivalic acid, the pyrolysis of the lead salts of this carboxylic acid is particularly suitable because in this procedure the lactone is obtained under mild conditions in a relatively good yield. However, in view of the economy of the process it is desirable to convert the lead chloride formed in the reaction by reacting it with alkali bases in order to convert it into lead oxide which is needed for the preparation of the chloropivalic acid lead salts, so that in this procedure only chloropivalic acid and alkali base are consumed in the production of pivalolactone. However, a re-conversion of the solid final product of pyrolysis is logical in a commercial process only if in the pyrolysis of the lead salt, lactone and lead chloride are obtained in almost quantitative yield.

It has now been found that pivalolactone can be obtained with particular advantage by a continuous process from the lead salt of chloropivalic acid. In this process a reaction space containing an endless conveyer or platform conveyer consisting of chain-link-like elements is used and the lead salt of the chloropivalic acidwhich is in dry, pulverulent or fine-grained formis heated under reduced pressure of 1100 torr, preferably 1-15 torr, under exclusion of oxygen in a layer having a thickness of 0.1-3 cm., preferably 0.3-1.5 cm. Said lead salt of chloropivalic acid is charged to the endless conveyer band or the platform conveyer, exposed in the reaction space to a temperature in the range of 200-400 C., preferably 300360 C. and is passed under these temperature conditions through the reaction space. The gaseous pivalolactone formed by pyrolysis is separated and recovered.

It has been unexpectedly found that under the above described conditions pivalolactone can be obtained in yields of 95% of the theory, which is not possible in the discontinuous preparation. An essential condition of an almost quantitative yield of pivalolactone according to this invention consists in that heating of the lead salt is carried out at a small thickness of maximum 3 cm. of the salt layer. If this thickness of the layer is exceeded, for example at a thickness of greater than 3 up to 10 cm., the lactone is obtained in considerably lower yields.

The lead chloride resulting from the continuous decomposition of the lead salt is capable of trickling and can be converted, e.g. by means of sodium hydroxide solution, into Pb O. It has been found to be of advantage to extract unconverted lead salt of chloropivalic acid, which is present in the lead chloride in a small amount, prior to the treatment with sodium hydroxide solution, by means of acetone or methanol.

In order to carry out the continuous process according to this invention successfully, and to obtain the pivalolactone formed almost completely, it is indispensable that oxygen be excluded from the reaction space which is under reduced pressure. It has been found that even small amounts of oxygen which may enter the reaction space due to leakiness of the apparatus, cause decomposition in the reaction space at a temperature range of 200-400 C. of the lactone formed, into isobutene and carbon dioxide and also to carbon monoxide and other hydrocarbons.

Devices for continuous splitting of pulverulent starting materials into a solid product and a gaseous component have been known from the prior art. For example, the German Patent No. 579,468 describes the continuous decomposition of loose material in a cylindrical oven provided with resistance heating and a platform conveyer composed of chain-link-like elements.

A process for the thermal treatment of materials which can be easily decomposed, under vacuum or in a specific gaseous atmosphere-has been likewise described. In this process the solid starting material is passed by means of shaking channels or conveyer bands between heating elements having the shape of a hairpin curve (see German Patent 571,894).

The above mentioned processes and devices are used for the thermal treatment of inorganic materials which are liable to decompose, such as fiuosilicates, nitrates, chlorides, carbonates, or for roasting metal sulfides. However, nothing could be infe'rred from the above mentioned prior art disclosures as to how the problem of the present invention can be solved.

Moreover, it is a surprising efiect that upon meeting the conditions of the present invention, as described above, the pivalolactone can be obtained in almost quantitative yield. I

The appended drawings diagrammatically illustrate a device in which the continuous pyrolysis process according to the present invention can be carried out. In order to attain a quick removal and cooling of the gaseous lactone from the reaction space discharge ducts are provided for the gaseous reaction product along the entire length of the conveyer band.

It has been found to be of advantage to introduce small amounts of nitrogen into the lowe-r part of the reaction space in order to create a permanent gas stream in the direction of the condensation apparatus connected with the beforementioned discharge ducts.

In the appended diagrammatic drawings:

FIG. 1 is a diagrammatic view, in side elevation, partially broken away, of an apparatus suitable for carrying out the process of this invention;

FIG. 2 is a detail of the conveyer drive in plane view;

FIGS. 3 and 3a are plan and side elevation views, respectively, of the dosage disc; and

FIG. 4 is a sectional view of the reaction chamber taken along line 4-4 of FIG. 1.

The dry, pulverulent lead-II-chloro-pivalate is introduced into the reaction space by known processes for continuously charging solid starting materials into a vacuum zone under exclusion of oxygen of the atmosphere and is uniformly spread with the above described thickness of the layer on the endless conveyer band 6. The band which consists of heat-resistant sheet steel or of a platform conveyer formed by chain-link-like members which intermesh with each other, is preferably conducted over a heated base or support 8 provided with rollers, and over the guide rollers 9 and 17, provided at the ends of the base 8. The heating of the base or support which may consist, for example, of aluminum, is preferably brought about by an electrical resistance heating system. It will be appreciated that the heat needed for bringing about pyrolysis can be supplied also by other means, e.g. suitable hot gases or liquids. Loading of the transport band takes place over a dosage device, by means of which the lead salt is uniformly distributed in the desired thickness of the layer on the band. In a wall of the reaction space a window is provided for checking the loading or charging of the lead salt.

The pulverulent reaction product is separated at the guide roller 17 from the band by means of a scraper, falls into a receiving container 19. From the latter, it isremoved by means of a sluice system (or air lock system) from the apparatus which operates under vacuum.

Example 1 In order to prepare lead-II-chloropivalate, 1092 g. of chloropivalic acid are dissolved in 2200 cm. of heptane. To the solution which is 40-50 C. warm, during one hour 938 g. of pulverulent lead-II-oxide are added under vigorous stirring and the resulting mixture is heated for 5 additional hours to 50 C. in order to complete the conversion of choloropivalic acid into the lead salt.

The precipitated lead-II-chloropivalate-which still contains small amounts of the lead oxide added in excess-is filtered off and dried under vacuum at 50 C. 890 g. of the lead salt of chloropivalic acid-which contain 46 g. of unconverted lead oxide-are thus obtained. As the lead salt is somewhat soluble in the solvent used, the heptane solution obtained by filtration is preferably used again in the preparation of lead-II-chloropivalate.

In carrying out the process, container 1 is filled with comminuted, pulverulent or fine-grained lead-chloropivalate, evacuated, then filled with nitrogen and then evacuated again. From container 1, the lead salt passes over a vacuum slide into a dosage device 2, in which it is kept in movement, in order to prevent caking or agglomeration, by means of a stirrer 3.

At the dosage disc 4 provided with knife-like scrapers (see FIG. 3), the salt is continuously withdrawn from dosage device 2 and applied with a uniform thickness of the layer to the endless steel band 6 arranged on the pyrolysis reactor 8. The steel band is tensioned by the tensioning device 7 on the heating block 8, which may have a length of e.g. 110 cm., is driven by an electromotor over a vacuum rotary bushing 10. On the heating block lateral limiting strips are provided in order to guide the band 6 and to prevent sliding off of the solid material (see FIG. 4). The uniform spreading of the lead salt can be checked through the window 11. Over the entire length of the heating block 8, plate-like electric heating elements 12 are arranged, so that the steel band is uniformly heated.

The salt resting on hand 6 passes through the heated pyrolysis reactor which is under vaccum, is split during this passage into solid lead chloride and gaseous pivalolactone. The latter enters the discharge openings 13, passes from these openings to the cooling devices 14, 15, 16 and is condensed therein. The solid product of pyrolysis is removed from hand 16 at the guide roller 17 by means of a scraper 18, falls into container 19, from which it is discharged over an air lock 20. In order to accelerate removal of the lactone vapors from the hot reaction zone in pyrolysis chamber 5, some nitrogen gas is continuously introduced into the reactor through tube 21.

In the apparatus described above and shown in the drawing e.g. 4,000 g. lead salt of chloropivalic acid, which contain 2.4% lead oxide, are subjected to pyrolysis at a temperature of 330 C. under a vacuum of 3 torr. Thereby, the lead salt of chloropivalic acid is charged to the heated steel band 6 in a layer of 2 mm. thickness. The solid final product discharged over the air lock 20 contains 179 g. unconverted lead chloropivalate which is easily recovered by extraction with organic solvents, e.g. methanol. In order to completely recover the lactone formed by pyrolysis, the condensers 15 and 16 are cooled to 10 and 30 C., respectively. A total of 1560 g. of pivalolactone is thus obtained, which corresponds to 94% of the theory, based on the converted amount.

Example 2 In the manner and in the apparatus disclosed in the above Example 1, 4000 g. of the lead salt of chloropivalic acid are subjected to pyrolysis at a temperature of 360 C. and in a vacuum of 5 torr within 6 hours. The solid final product contains 351 g. of unconverted lead chloropivalate. 1,321 g. (89% of the theoretical yield, based on the amount of converted lead salt) are thus obtained.

It will be understood that the process of this invention may be carried out with various modifications within the scope of the appended claims. The vacuum locks for introducing the starting material into the evacuated reaction space are designed in conventional manner. The amount of nitrogen to be continuously introduced into the reaction space varies between 0 and 500% by volume based on the volume of the gaseous pivalolactone to be formed and removed from the reaction space. Instead of heptane, other organic solvents, such as acetonitrile, benzene, n-dibutylether can be used for dissolving the chloropivalic acid to be converted into its salt.

The parts mentioned herein are by weight if not otherwise stated.

What is claimed is:

1. Process for producing pivalolactone by thermal decomposition of the lead salt of chlo-ropivalic acid, comprising passing said salt in dry, finely distributed condition through a reaction space, from which free oxygen is excluded, under a reduced pressure of 1-100 torr, at a temperature in the range of ZOO-400 C., in a layer of 0.1-3 cm. thickness, until most of said salt is converted into solid lead chloride and gaseous pivalolactone, discharging said gaseous pivalolactone from said reaction space, and subjecting it to liquefying by cooling.

2. Process for producing pivalolactone, as claimed in claim 1, in which in the reaction space a vacuum of l-5 torr is maintained.

3. Process for producing pivalolactone, as claimed in claim 1, in which the thickness of the layer is in the range of 0.3-1.5 cm.

4. Process for producing pivalolactone, as claimed in claim 1, in which the temperature of the reaction space is in the range of 300-360 C.

5. Process for producing pivalol-actone, as claimed in claim 1, in which a small amount of nitrogen is continuously introduced into the reaction space in order to accelerate removal of the pivalolactone vapors from the reaction space.

6. Process for producing pivalolactone, as claimed in claim 1, in which the pivalolactone vapors discharged from the reaction space are cooled to a temperature in the range of 10 to 30 C.

7. Process for producing pivalolactone, as claimed in claim 1, in which the solid lead chloride formed in the reaction space is converted with aqueous sodium hydroxide solution into lead -oxide, and used again in the process.

lead -chloropivalate present in the lead -chloride formed in the reaction space is extracted with an organic solvent from said lead -chloride.

References Cited by the Examiner UNITED STATES PATENTS 3/1961 Reynolds et a1. 260343.9

OTHER REFERENCES Weissberger: Technique of Organic Chemistry: Distillation, vol. IV (1951), pages 500 and 501.

ALEX MAZEL, Primary Examiner.

8. Process as claimed in claim 7, in which unconverted 15 JOSEPH NARCAVAGE, Assistant Examinel 

1. PROCESS FOR PRODUCING PIVALOLACTONE BY THERMAL DECOMPOSITION OF THE LEAD**II SALT OF CHLOROPIVALIC ACID, COMPRISING PASSING SAID SALT IN DRY, FINELY DISTRIBUTED CONDITION THROUGH A REACTION SPACE, FROM WHICH FREE OXYGEN IS EXCLUDED, UNDER A REDUCED PRESSURE OF 1-100 TORR, AT A TEMPERATURE IN THE RANGE OF 200-400*C., IN A LAYER OF 0.1-3 CM. THICKNESS, UNTIL MOST OF SAID SALT IS CONVERTED INTO SOLID LEAD**II CHLORIDE AND GASEOUS PIVALOLACTONE, DISCHARGING SAID GASEOUS PIVALOLACTONE FROM SAID REACTION SPACE, AND SUBJECTING IT TO LIQUEFYING BY COOLING. 